Corning Incorporated has developed a process known as the fusion process (e.g., downdraw process) to form high quality thin glass sheets that can be used in a variety of devices like flat panel displays (e.g., flat panel liquid crystal displays). The fusion process is the preferred technique for producing glass sheets used in flat panel displays because the glass sheets produced by this process have surfaces with superior flatness and smoothness when compared to glass sheets that are produced by other methods. The fusion process is briefly described below with respect to FIG. 1 (PRIOR ART) but for a more detailed description about the fusion process reference is made to co-assigned U.S. Pat. Nos. 3,338,696 and 3,682,609. The contents of these documents are hereby incorporated by reference herein.
Referring to FIG. 1 (PRIOR ART), there is shown a schematic view of an exemplary glass manufacturing system 100 which utilizes the fusion process to make a glass sheet 138. As shown, the exemplary glass manufacturing system 100 includes a melting vessel 102, a fining vessel 104, a mixing vessel 106 (e.g., stir chamber 106), a delivery vessel 108 (e.g., bowl 108), a fusion draw machine (FDM) 110, and a traveling anvil machine (TAM) 112. Typically, the components 104, 106 and 108 are made from platinum or platinum-containing metals such as platinum-rhodium, platinum-iridium and combinations thereof, but they may also comprise other refractory metals such as molybdenum, palladium, rhenium, tantalum, titanium, tungsten, or alloys thereof.
The melting vessel 102 is where the glass batch materials are introduced as shown by arrow 114 and melted to form molten glass 116. The melting vessel 102 is connected to the fining vessel 104 (e.g., finer tube 104) by a melting to fining vessel connecting tube 113. The fining vessel 104 has a high temperature processing area that receives the molten glass 116 (not shown at this point) from the melting vessel 102 and in which bubbles are removed from the molten glass 116. The fining vessel 104 is connected to the mixing vessel 106 (e.g., stir chamber 106) by a finer to stir chamber connecting tube 118. And, the mixing vessel 106 is connected to the delivery vessel 108 by a stir chamber to bowl connecting tube 120. The delivery vessel 108 delivers the molten glass 116 through a downcomer 122 into the FDM 110 which includes an inlet 124, a forming vessel 126 (e.g., isopipe 126), and a pull roll assembly 128.
As shown, the molten glass 116 flows from the downcomer 122 into the inlet 124 which leads to the forming vessel 126 (e.g., isopipe 126) which is typically made from a ceramic or a glass-ceramic refractory material. The forming vessel 126 includes an opening 130 that receives the molten glass 116 which flows into a trough 132 and then overflows and runs down two lengthwise sides 134 (only one side shown) before fusing together at what is known as a root 136. The root 136 is where the two lengthwise sides 134 come together and where the two overflow walls of molten glass 116 rejoin (e.g., re-fuse) to form the glass sheet 138 which is then drawn downward by the pull roll assembly 128. The pull roll assembly 128 delivers the drawn glass sheet 138 which, at this point in the process, is substantially flat but later in the process typically develops a slightly curved/bowed shape across the glass sheet 138. This bowed shape may remain in the glass sheet 138 all the way to the TAM 112. The TAM 112 has a mechanical scoring device 146 (e.g., scoring wheel 146) and a nosing device 148 which are used to mechanically score the drawn glass sheet 138 so it can then be separated into distinct pieces of glass sheets 142. The TAM 112 is located in an area referred to herein as a bottom of the draw 140 (BOD 140).
The TAM's 112 scoring and separating processes cause motion in the glass sheet 138 at the BOD 140 which contributes to the creation of undesirable stress, position and shape variations within the glass sheet 138 in the forming region located up near the FDM 110. For instance, it has been seen during the scoring and separating processes that the glass sheet 138 generally moves back-and-forth by more than 5 mm. There are several problems which can occur whenever the glass sheet 138 distorts or warps due to the sheet shape, position and motions changes etc. . . . caused during the BOD 140 sheet separation (scoring, bending, separating etc. . . . ) processes. For instance, changes in sheet shape, position and motion can detrimentally affect the forming process in the FDM 110. This is because the conditions of the glass in the FDM 110 are tightly controlled in a steady state manner during the forming process using elements such as radiant and conductive heating or cooling elements, and contact and non-contact positioning and drawing mechanisms. Thus, if the position or shape of the glass sheet 138 varies beyond acceptable limits, then this tight control is disrupted and the conditions of the glass may vary resulting in unacceptable glass formation in the FDM 100. In addition, the resulting glass sheets 138 which vary in shape from sheet to sheet is not a desirable situation for the customers. Furthermore, the scoring device 146 in the BOD 140 must follow the curvature/bow of the glass sheet 138 to properly score the glass sheet 138. Thus, if the sheet shape varies beyond acceptable limits then the scoring device 146 may not adequately score the glass sheet 138 without the use of complex and expensive sheet shape detection devices and variable path-motion scoring equipment within the BOD 140. Accordingly, there is a need for a device that stabilizes the glass sheet 138 and maintains accurate positional, shape and motion control of the glass sheet 138 at both the FDM 110 and BOD 140. The impact of such a device will be especially significant for tall draw or large size platforms, such as Gen 7 and larger, where the distance between FDM 110 and TAM 140 is relatively long or the width of the glass sheet 138 is relatively large. This need and other needs are satisfied by the stabilizing system, the glass manufacturing system, and the manufacturing method of the present invention.